Method for drying compressed air



Dec. 24, 1968 v. Q. RAPP 3,417,547

METHOD FOR DRYING COMPRESSED AIR Filed Dec. 7, 1966 2 Sheets-Sheet l I N VE N TOR.

V/A/C'EA/T 4 04 M771; HOFKMAA/M Fail/6P 2.46/4/4 6 ea. 24, 1968 v, RAPP METHOD FOR DRYING COMPRESSED AIR 2 Sheets-Sheet 2 Filed Dec. 7, 1966 BY M4775; Han n 1 4444 fi'lSf/ffifl/E/A/Q' ArraeMexr United States Patent 3,417,547 METHOD FOR DRYING COMPRESSED AIR Vincent Q. Rapp, Erie, Pa., assignor to General-Erie Corp. Filed Dec. 7, 1966, Ser. No. 599,884 2 Claims. (Cl. 5527) ABSTRACT OF THE DISCLOSURE A method for drying compressed air by passing the hot compressed air through two cooling zones. The compressed air is then expanded and passed through a nonregenerative moisture adsorbing means. In the first cooling zone the cooled compressed air is heat exchanged with the hot compressed air.

BACKGROUND 1) Field of the inventi0n.This invention relates to the art of conditioning compressed air for industrial uses and it is particularly concerned with a new method of, and new apparatus for, cooling and drying compressed air and reducing its dew point to about -50 F. at atmospheric pressure or about 3 F. at 100 p.s.i.g.

(2) Description of the prior art.The most nearly pertinent prior art with which I am familiar is my patent No. 3,180,072 which issued on April 27, 1965.

While air conditioners embodying the invention of that patent have been commercially successful, they have certain operational characteristics and disadvantages which limit the extent of their applicability. One such disadvantage is that they require considerable amounts of cooling water which is not always available in all areas where they are needed. If adequate amounts of cooling water are not avilable, other chilling devices must be employed which are costly to purchase, operate and maintain.

A main characteristic of dryers of the type disclosed in the aforesaid patent is that it was necessary to cool the hot compressed air to about 90 F. before it entered the dryer in order to attain a dew point of about 43 F. at 100 pounds per square inch (p.s.i.g.) or about 4 F. at atmospheric pressure. Much lower dew points have been desired.

SUMMARY In contrast with the prior art, the present invention avoids the disadvantages of employing cooling water or special means for cooling the hot compressed air, is capable of accepting compressed air at a temperature of about 200 F. to about 250 F. and of discharging it at about 90 F. to about 120 F. with a dew point as low as about 50 F. at atmospheric pressure or about 3 F. at 100 p.s.i.g.

Moreover, the air flow is about 50% greater than that in the apparatus of the above identified patent with relatively small loss of efficiency, and full capacity flow can be maintained for indefinite periods with an overload of up to approximately 30% without any great loss of drying efficiency or the creation of a freeze-up within the refrigerating system.

Another advantage of the present invention is that it is able to separate from the air and discharge from the system all but less than about 5 parts per million of the widely varying amounts of oil in compressed air.

A further advantage is that the consumption of desiccant is reduced from about to about by the present invention as compared with the consumption experienced with the prior art devices. By reason of this decreased consumption, only one addition of desiccant per year shift is required by apparatus embodying the present invention as contrasted with the addition of "ice greater amounts, from two to four times per year per shift with the prior art devices.

THE DRAWINGS The present invention will be better understood by those skilled in the art from the following specification and the drawings accompanying it in which:

FIG. 1 is a side elevational view, partly in section, of apparatus embodying the present apparatus invention;

FIG. 2 is a top, plan view of the apparatus of FIG. 1;

FIG. 3 is a side elevational view, partly in section, of the second cooler and portions of the refrigerator of the apparatus of FIG. 1;

FIG. 4 is a fragmentary, sectional view taken on line 44 of FIG. 2;

FIG. '5 is a diagrammatic view of the refrigerator part of the apparatus invention; and

FIG. 6 is a diagrammatic view showing the flow of air and cooling fluids in the apparatus of FIGS. 1 to 4 and indicating the steps of the present method invention.

In FIGS. 1 to 4, 1 designates a sheet metal, box-like housing having a closed bottom supported by skids 2 and an open top. A first cooler 3, a second cooler 5, a dryer 7 and a refrigerant cooler 9 are disposed within the housing. The dryer 7 rests on the bottom of the housing 1 and extends vertically upward along one end of the housing 1. The first cooler 3 is positioned at one side of dryer 7 and above the cooler 9. A partition 11, consisting of a horizontal part 11a and a vertical part 11b, partially divides the interior of the housing 1 into compartments, the first cooler 3 being positioned in one compartment and the dryer and cooler being positioned in the other compartment. Sheet metal vertical and horizontal walls 12 are attached to the bottom, side and end walls of housing 1 and together with those walls form an enclosure for the refrigerant cooler 9. Screened openings (not shown) in the end and side walls of the housing I serve to permit flow of fan-propelled ambient air over parts of the refrigerant cooler.

The first cooler 3 consists primarily of a tube within a tube. The inner tube 15 is within the outer tube 17 and these two tubes provide an annular space 19 therebetween for air flow. An inlet 20 serves to conduct heated compressed air into annular space 19. The tubes 15 and 17 of first cooler 3 are coiled to form a circle. Screened openings (not shown), of about the same diameter as the inner diameter of the coils of tubes 15 and 17, serve to permit flow of fan-propelled air past the coils for cooling the heated air flowing in the annular passage 19. A fan (not shown) may be positioned within the housing be tween the coils and the opening in one side of the housing.

The outlet end of tube 17 is connected, as by elbow 21, to the second cooler 5. Cooler 5, like cooler 3, consists primarily of a tube within a tube. 23 indicates the inner tube, 25 the outer tube and 27 indicates an annular space between the two tubes. Cooler 5 is coiled around and closely adjacent to the vertical side of dryer 7 and inner tube 23 is open at its lower end Within dryer 7 as at 28 and below transverse partition 29 which supports a deliquescent desiccant on its upper surface and which has a drain outlet 30 for dissolved desiccant to flow into the lower part of the dryer. The air discharged from tube 23 impinges against the liquid desiccant as it passes through opening 30 and propels that liquid with considerable velocity against the opposite surface of the dryer, thereby breaking up globules of the desiccant and exposing previously unsaturated parts of the desiccant to the moisturedirt, pollen, bacteria and other contaminants in the air. In this manner excessive maintenance costs caused by sludging or corosion of air tools and the like may be avoided.

While any suitable deliquescent desiccant may be used in carrying out the invention, I prefer to use a desiccant consisting of about 90% urea in shot form, between about 1% and about of ammonium chloride and between about A% and about /2% of a corrosion inhibitor, for example, sodium borate containing about 4% of sodium nitrite.

Pipe 32 connects the upper end of dryer 7 with the interior of pipe from which the air may be drawn off through fitting 32a for industrial use.

The refrigerant cooler 9 is connected to the second cooler 5 by a tube 33 which carries cold expanding refrigerant into the annular space 27 between tubes 23 and 25 and tube 35 returns that refrigerant from the other end of cooler 5 to the refrigerant cooler.

FIG. 5 shows diagrammatically a refrigerating unit or refrigerant cooler which may be used as unit 9 of apparatus embodying the present invention. In this figure, 45 indicates an hermetically sealed metal case housing enclosing a motor 46 and a piston 47 actuated thereby to compress a refrigerant. Any suitable refrigerant, for'example Freon, may be compressed by compressor 45. Pipe line 57 is connected to the output side of the compressor and the coiled portion 59 of that tube is provided with cooling fins 61 against which cooling air may be blown, as by fan 63. Tube 57 is connected to a heat exchanger 64 which, in turn, is connected to a tube 65. This tube is provided with a pressure reducing valve 66 and then with a filter (not shown) and communicates with tube 33, above mentioned. Pipe line 35 passes through an accumulator 67 of conventional form and then extends through heat exchanger 64 and returns to the compressor 45. Back seated valves 71 in line 57 and 73 in line 35 serve to control the compressor by being connected to suitable switches (not shown). Valve 71 serves to energize the compression motor when the pressure on the refrigerant has reached a predetermined low value while valve 73 serves to de-energize the compression motor when the pressure has reached a predetermined high value.

The method of the present invention is diagrammatically illustrated in FIG. 6. Compressed air at a temperature of between about 200 F. and about 250 F. is passed through pipe into the annular space 19 between tubes 15 and 17 of the first cooler 3, Le, the first cooling zone. This air flows through that space and thence through line 21 and into the inner tube 23 of the second cooler 5, i.e., the second cooling zone. In the first cooler 3, the temperature of the compressed air is reduced to about 90 F. or about 120 F. depending on its entering temperature. The thus cooled air flows through inner pipe 23 of the second cooler 5, i.e., the second cooling zone and discharges into the lower end of dryer 7, as at 28. The temperature of the compressed air is reduced in cooler 5 from its entering temperature of about 90 F. to about 120 F. and is discharged into the dryer 7 at a temperature of about 40 F. In this dryer, or drying zone, moisture is removed from the air as it passes through the bed of desiccant and the dew point of the air is reduced by the desiccant to between about F. and about -50 F. at atmospheric pressure or to about -40 F. at atmospheric pressure and about 3 F. at a pressure of 100 p.s.i.g. This cooled and dried air then passes through the inner tube 15 of the first cooler where it is reheated to about 100 F. in passing in countercurrent flow heat transferring relation to the heated compressed air flowing in the annular space 19.

The partially cooled compressed air discharged from the first cooling zone flows in countercurrent flow relative to and in heat exchanging relation to the expanding cold refrigerant flowing through the expansion valve 66 of the refrigerating unit. The refrigerant which is warmed by extracting heat from the air flowing in pipe 23 is returned to the refrigerating compressor and recompressed, cooled and then expanded into line 33 of the secondary cooling zone.

It will be understood from the foregoing specification that apparatus embodying the present invention is simple in construction, is devoid of moving parts except in the refrigerating unit, effectively cools compressed air from an entering temperature of up to about 250 F. to a discharge temperature of about 100 F. and thereby lowers the dew point to between about 25 F. and -50 F. at atmospheric pressure. It will also be understood that no water is employed for cooling the compressed air and, hence, that the apparatus may be employed even in arid regions.

It will also be understood that oil in the compressed air is removed more or less completely with the liquid desiccant which flows out of the dryer, thus making it unnecessary to provide the usual and costly elaborate oil filters for removing such oil.

Apparatus embodying the present invention may be readily handled for it is mounted on skids and may be picked up and transported by a lift truck.

Apparatus embodying the present invention is capable of operating at as much as 30% over rated capacity without a great loss of efliciency or a freezing of the refrigerant and the volume of air flow may be increased as much as 50% with relatively little loss of efliciency. When the apparatus is designed for a maximum air temperature of about 200 F., temperatures of as high as 250 F. may be accommodated with little loss of efliciency.

Having thus described this invention in such full, clear, concise and exact terms as to enable any person skilled in the art to which it pertains to make and use the same, and having set forth the best mode contemplated of carrying out this invention, I state that the subject matter which I regard as being my invention is particularly pointed out and distinctly claimed in what is claimed, it being understood that equivalents ormodifications of, or substitutions for, parts of the above specifically described embodiment of the invention may be made without departing from the scope of the invention as set forth in what is claimed.

What is claimed is:

1. The method of conditioning compressed air for industrial uses which comprises the steps of (a) cooling a stream of highly heated compressed air by passing it through a cooling zone in heat exchanging relation to the air after it has been cooled and dried,

(b) further cooling the thus cooled air by passing it in heat exchanging relation with a closed circuit refrigerant,

(c) removing liquid from the thus cooled air by expanding it,

(d) drying the air by passing it through nonregenerative moisture absorbing means,

(e) and then reheating the thus dried air by passing it through the cooling zone in heat exchanging relation to the highly heated compressed air flowing through the cooling zone.

2. The method of conditioning compressed air for industrial uses which comprises the steps of (a) passing a stream of compressed air at a temperature of about 250 F. through a cooling zone including a heat exchanger and cooling the air to between about F. and about 120 F.,

(b) further cooling the air to about 40 F. by passing it in heat exchanging relation with a closed circuit refrigerant,

(c) removing liquid from the thus cooled air by expanding it,

(d) drying the air and reducing its dew point to about -3 F. at p.s.i.g. by passing it through nonregenerative moisture absorbing means,

(e) and reheating the thus dried air to about 100 F.

by passing it through the cooling zone in heat exchanging relation to the compressed air flowing FOREIG N PATENTS 654,801 12/1962 Canada.

through the cooling zone.

5 REUBEN FRIEDMAN, Primary Examiner.

References Cited UNITED STATES PATENTS C. N. HART, Assistant Examiner.

Hasche 5535 Kiyonaga et all 5558 US' X'R' Rapp 55269 10 55-269, 35, 388

Dennis 62-14 

